The ACAS 570 interactive laser cytometer will provide Dartmouth Medical School and Dartmouth College with the capacity to: 1) spatially and temporally resolve fluorescence on individual cells; 2) study and quantitate cell-cell interactions; 3) isolate adherent cells that are present in a population at low frequencies; 4) reconstruct the distribution of specific antigens on the surface of cells or within cells by confocal imaging; 5) determine the rates and extent of antigen translocation by fluorescence recovery after photobleaching and 6) examine the biological and biochemical responses of individual cells through the use of probes that are sensitive to changes in cellular biochemistry. Request for the purchase of an ACAS 570 is supported by 16 NIH-funded investigators in the Departments of Microbiology, Biochemistry, Pharmacology, Medicine, and Physiology at Dartmouth Medical School and in the Department of Biology at Dartmouth College. The ACAS 570 will provide essential instrumentation in support of 29 NIH-supported projects. These projects include: 1) the analysis of intercellular communication between helper T lymphocytes and B lymphocytes, 2) the regulation of Ca++ transport in parathyroid-sensitive cells, 3)cellular mechanisms of renal distal tubule ion transport, 4) the regulation of mitosis in see urchin embryos, 5) studies into the mechanisms of cytotoxic T lymphocyte (CTL) recognition of virally-transformed target cells, 6) the analysis of the mechanisms of monocyte (effector cell)-mediated lysis of target cells via receptors for Ig (FcR), 7) the resolution of differences between daughter cells during the mitosis of T lymphocytes, 8) studies of ion transport in collecting duct cells, 9) the study of Ca++ transients in cells bearing FcR, 10) the mechanisms of recognition of leukemia antigen by antiviral CTL, 11) the regulation of ion channel distribution at synapses, 12) the regulation of acetyl CoA carboxylase in hepatoma cells, 13) the selection of clones stably expressing androgen receptor and 14) studies into the control of neuronal excitability by neurotrophic factors. The important biological questions raised by these proposals can only be addressed with the advanced interactive capabilities of the ACAS 570.